The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a hybrid vehicle includes both an electric motor and an internal combustion engine as a power source, and since both the internal combustion engine and the motor are used, large rotation torque may be used at low speeds, and when driven by the electric motor, the hybrid vehicle generates a small amount of noise and does not emit a harmful gas. Also, since the internal combustion engine is limitedly used when desired or in a region with high efficiency, the hybrid vehicle may be designed to have a low fuel consumption rate in spite of a compact size and also convert kinetic energy to electric energy under brake operation.
A vehicle may be driven by one gasoline engine and two motors, which are mechanically connected by a planetary gear device and a differential gear device for a driving wheel, and one of two motors is connected to the differential gear by a driving chain or a gear. This system is referred as to a hybrid system.
An oil pump system including a plurality of oil pumps is applied to a transmission of the hybrid vehicle to supply oil to lubricate friction lubrication elements (e.g., a bearing, a bush, a gear, and the like), to cool cooling elements (e.g., an electric motor, or the like), or to form control pressure of operational elements (e.g., a clutch, a brake, and the like).
Flow rate characteristics of oil consumed for each element are varied according to operational conditions of a vehicle, or the like. For example, a quantity of oil consumed for lubricating a friction lubrication element may be increased in proportion to a vehicle speed, a quantity of oil consumed for cooling a cooling element may be increased when torque of an electric motor is increased in a climbing/acceleration condition of a vehicle, and the like, and a quantity of oil consumed for forming control pressure of an operating element may be increased at the time of transmission.
In the related art, we have discovered that it is very difficult to control a flow rate of an oil pump according to operational conditions such as an operation mode, a motor temperature, and the like, and the efficiency of the control is degraded.